It is well known that windshield wiper blades are driven in contact with the windshield of a motor vehicle, over a given sector of the latter and with a predetermined pressure, by means of a windshield wiper arm which is coupled to a drive unit having a motor that drives a speed reducing means, and which transforms the initial rotary movement of the motor directly or indirectly into alternating or oscillating motion of the drive shaft and wiper arm.
The drive unit conventionally has an electric motor, the rotor of which extends along the interior of a closed casing, the speed reducing means generally comprising a gearing system, with one of the gears being coupled, either directly or through a crank and connecting rod system, to the drive shaft which projects outside the casing of the drive unit, and which serves to actuate the windshield wiper arm.
As is again already known, the gear system carries, inter alia, on one of its toothed wheels, electrical contacts which enable the windshield wiper arm or arms to be selectively driven at variable speeds, and to be stopped, in such a way that the wipers will always be parked in a fixed lower position so as not to interfere with the visibility of the driver of the vehicle.
The drive shaft projects from the surface of the vehicle bodywork, and the presence of the above mentioned electrical contacts necessitates that the drive shaft must be mounted so that it is sealed from the ingress of water or impurities, so as to ensure that no short circuiting will occur within the drive unit. Such an arrangement is described in the specification of French published patent application No. FR 2 165 540A, in which the motor shaft is surrounded by a sleeve, the anterior portion of which (i.e. the portion remote from the speed reducing means) has an opening into which an O-ring seal can be introduced, together with a bearing comprising a ring of a material having a low coefficient of friction. The O-ring seal bears, at the side of the motor/speed reducing means, on a shoulder, and is retained opposite to the shoulder in an axial position by means of a member which is fitted at the front of the sleeve. This member is itself retained in the sleeve by means of a circlip or by any other similar retaining means.
Although such a mounting works very well in practice, it is relatively costly, in particular to the extent that it requires a substantial amount of machining, and also the fitting of an additional member which has to be retained in position by fastening or retaining means, which also have to be fitted and which increase manufacturing costs.